Conventionally, the alkaline secondary battery has the electric power generation element by spirally rolling-up the positive electrode formed by pasting and drying the paste having nickel oxide as the main component to the substrate, and the negative electrode formed by pasting and drying the paste having cadmium and hydrogen absorbing alloy powder as the main component by providing the separator of non-woven fabric such as polyethylene, polypropylene or so therebetween.
Also, the lithium secondary battery has the electric power generating element by spirally rolling-up the positive electrode and the negative electrode comprising the active material layer capable of absorbing and releasing the lithium ion reversibly, and providing the separator therebetween.
This electric power generating element is pressure inserted into the metal container of cylinder shape or a square shape having a widely opened opening part, and the electrolytic solution having high concentration and high viscosity is introduced, and it is sealed by the sealing cap of sealing cover or so via the insulation gasket followed by reducing the diameter of the opening part of the metal container and bending the opening end inward; thereby the battery is sealed. Between the insulation gasket and the inner face of the opening part of the metal container, the sealing layer is formed by pasting the sealing material composition for further secure seal.
However, at the surface of the inside of the opening part of the metal container which is usually used, there are minute roughness in the longitudinal direction formed during the squeeze processing, thus the sealing material composition having adhesiveness may not be able to sufficiently embedded to the bottom of the roughness; therefore the electrolytic solution introduced in the battery may leak out from the battery due to the electrocapillarity. Therefore, not only that it deteriorate the electric performance, but also the used machine will also be damaged by the alkaline electrolytic solution as well. Also, in the lithium secondary battery, the organic solvent is used as the solvent of the electrolytic solution, thus if the water enters inside the battery, it is known that the cycle characteristic will be significantly deteriorated.
The alkaline secondary battery and the lithium secondary battery are widely used for the automobile recently, and along with the expansion of the used range thereof, the higher safety than the conventionally used one is demanded even under an extremely harsh condition. For example, in case the temperature of the secondary battery becomes extremely high, or in case the pressure inside the battery becomes high, it is demanded to have no damage to the machine caused by the leakage of the electrolytic solution. Various methods are being examined in order to obtain such characteristic, however the conventional seal material composition is still not sufficient enough, and higher level is being demanded in regards with the safety of the seal material itself at high temperature, the satability of the electrolytic solution or the metal container material, and the leakage prevention property of the electrolytic solutions.
In order to satisfy such demand, the use of the special seal material, the improvement of the crimp type, the strengthening of the sealing pressure, and the improvement of the insulation gasket or so are being examined. For example, as for the sealing material, pitch, tar, asphalt; the mixture of poly sulfonated ethylene with tar or asphalt; mercaptan expressed by RSH (R is alkyl group); poly vinyleden fluoride; the composition made of asphalt added with grease including the metal soap having one or more of metal selected from the group consisting of calcium, lithium, and barium; the mixture of curing agent and the urethane liquid rubber having the polybutadiene as the base; and those of half-dried polyamide resin or so dissolved or dispersed in the solvent, thereby the electrolytic solution is being prevented from leaking.
Further, for example, Patent article 1 describes that the alkaline secondary battery having excellent safety which does not allow the leakage of the electrolytic solution or the water intrusion can be obtained by sealing the seal part with the sealing material comprising the rubber of one or two or more selected from diene rubber and the rubber having the saturated main chain of polymethylene.
Patent article 2 describes the thermoplastic elastomer constituted from the block copolymer characterized by comprising two or more of glass transition temperatures; however the sealing material composition of Patent article 2 has a insufficient sealing property at the high temperature range.
Patent article 3 describes the method for sealing by elastomer made by mixing the predetermined appropriate amount of the curing agent with urethane liquid rubber having polybutadiene as the base; however in the sealing material of the patent article 3, the sealing property at the low temperature range is insufficient, hence further improvement is needed.
Patent article 4 describes that the secondary battery having significantly high safety with improved sealing property can be obtained by using the sealing material for the battery comprising the rubber having the saturated main chain of polymethylene type as the main component.
Patent article 5 describes that the secondary battery which can be used in wide range of environment with improved sealing property at high temperature can be obtained by using the sealing material for the battery comprising diene rubber having the weight average molecular weight of 10000 to 1500000 as the main component.